An internal combustion engine includes a piston which is moved by receiving explosive power from fuel combustion, and a cylinder which guides the movement of the piston. The cylinder is also called a gas column, and in a gasoline engine or a diesel engine, the piston is moved by explosive power generated by injecting fuel with air into the cylinder, and igniting and exploding fuel.
An inside or an inner wall of the cylinder is called a bore, and a wall surface of an inner wall of the cylinder is called a bore surface.
The piston unceasingly produces friction with the inner wall of the cylinder while being moved in the inside (bore) of the cylinder. Particularly, a piston ring is provided on a circumference of an upper portion of the piston to enhance close contact between the piston and the inner wall of the cylinder, and to prevent air or exploding fuel gas from leaking. The friction between the piston ring and the inner wall of the cylinder is particularly serious.
In general, the piston ring and the inner wall of the cylinder are relatively moved in parallel with each other by using lubricant that is called engine oil. Here, the engine oil forms a lubricative film between the piston ring and the inner wall of the cylinder and serves to reduce friction between the piston ring and the inner wall of the cylinder.
In general, it is a widely known fact from a theory of fluid lubrication that in a case in which two surfaces are in parallel like the inner wall of the cylinder and the piston, fluid dynamic pressure is not generated in lubricant even though the two surfaces are relatively moved by using liquid lubricant.
As such, the parallel relative movement of the cylinder and the piston is a movement that is difficult to form a lubricative film, and the cylinder and the piston are operated in a state in which the engine oil between the piston (or the piston ring) and the inner wall of the cylinder is always insufficient due to high combustion pressure and high combustion heat in the cylinder. For this reason, serious friction and abrasion occur between the piston ring and the inner wall of the cylinder. In a case in which the cylinder and the piston are operated under this driving condition for a long period of time, fuel consumption or engine oil consumption is increased, and of course, this may cause replacement of the engine in some cases.
In order to reduce the abrasion of the inner wall of the cylinder, which produces friction with the piston ring, a method of heat treatment, improving surface roughness, honing, or the like has been developed in the related art. However, as an operational environment of the engine is varied in a direction in which the piston ring is weakened against abrasion, a method of more efficiently reducing abrasion of the piston ring compared to the existing method is required.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.